1. Field of the Invention
The present invention relates to a toner and a method for producing the same, as well as a developer.
2. Description of the Related Art
In recent years, there appears a market for toners in which particle diameters thereof are downsized for producing high quality output images and the low-temperature fixing ability thereof is improved for saving energy consumed in the image forming process using the same.
Toners obtained by a conventional kneading and pulverization process are difficult to downsize, have indeterminate particle shapes and statistically dispersed particle diameter distributions, require large amounts of energy for fixation, and have other various problems. In particular, toners manufactured by the kneading and pulverization process have the following problem in fixation: toner particles manufactured by the kneading and pulverization process each frequently have in itself interfacing spaces which are filled with a releasing agent (wax) and at which each of the toner particles is cracked by pulverization, thus large surface areas of each of the toner particles produced by cracking are covered with the wax, which, while producing releasing effect, facilitates toner adhesion to carriers, photoconductors, and blades, leading to unsatisfactory performance thereof as a whole.
In order to solve the above-mentioned problems of the toners produced by the kneading and pulverization process, a toner production method using a polymerization process has been proposed.
When such a polymerization process is used, the toner particles being produced can be easily downsized and may have a particle size distribution with a size of statistical dispersion smaller than a size of statistical dispersion of a particle size distribution of toners produced by the pulverization process, and, further, a wax can be encapsulated in each of the toner particles.
For a production method for toner that employs such a polymerization process, a production method has been proposed by which a toner which contains, as a toner binder, products of an extension reaction of a urethane-modified polyester and which has a working sphericity of 0.90 to 1.00 for improving flowability, low-temperature fixing ability, and anti-hot offset property of the toner can be produced (e.g. Japanese Patent Application Laid-Open (JP-A) No. 11-133665).
In addition, a production method has been proposed by which a toner which is excellent in flowability as the toner powder and in transfer efficiency when the toner particles are downsized, and as well as excellent in every property of heat resistant storage stability, low-temperature fixing ability, and anti-hot offset property can be produced (e.g., JP-A Nos. 2002-287400 and 2002-351143).
Furthermore, a production method for a toner including maturing the toner for stabilizing the molecular weight distribution of a toner binder produced and for achieving both low-temperature fixing ability and anti-hot offset property in a balanced manner has been proposed (e.g., Japanese Patent (JP-B) No. 2579150 and JP-A No. 2001-158819).
Further, a production method is disclosed in which a crystalline polyester is introduced into a toner using the polymerization process for improving low-temperature fixing ability. In JP-A No. 08-176310, a method for preparing a dispersion using a solvent for phase separation is proposed as a method for preparing a dispersion of crystalline polyester. However, only a coarse dispersion having a dispersion particle diameter of several tens micrometers to several hundreds micrometers can be produced by the use of the proposed method for preparing a dispersion, and a dispersion that has a volume average particle diameter of 1.0 μm or less and that thus can be used in a toner, cannot be produced by the proposed method for preparing a dispersion. Further, in JP-A No. 2005-15589, an attempt to downsize the particle diameter of a dispersion of crystalline polyester is described in which only a crystalline polyester is mixed in a solvent and the resultant mixture is heated and cooled. However, the results of the attempt were unstable and insufficient.
A production method for a toner proposed in JP-A Nos. 11-133665, 2002-287400, and 2002-351143 is the method including addition polymerizing a polyester prepolymer having an isocyanate group with an amine in a reaction system composed of a mixture of an organic solvent and an aqueous medium for increasing the molecular weight of the polyester polymer.
Methods such as those mentioned above and toners obtained by the methods, however, have been insufficient for use, because, though they improve anti-hot offset property, they invite degradation of the low-temperature fixing ability and of the glossiness of images after fixation.
Similarly, although they can easily be applied to a polycondensation reaction which is a high-temperature reaction, production methods for a toner proposed in JP-B No. 2579150 and JP-A No. 2001-158819 cannot be applied to such reaction systems as mentioned above in which an organic solvent and an aqueous medium coexist, before various conditions are earnestly tested and satisfied for successfully achieving the application.
Also, in JP-A No. 08-176310 and JP-A No. 2005-15589, a crystalline polyester is introduced into a toner which is produced using a polymerization process for improving the low-temperature fixing ability, however, a dispersion having downsized particle diameters cannot be stably obtained, which results in degradation of the particle size distribution of the toner, making the procedure inadequate for achieving the production of a desired toner.